Three changes to the chart, plus one icon fix.
## Captions above the bar
Captions sat below their bar so the ribbons could leave from the bottom of the whole block without crossing them. They now sit above the bar and are painted over the ribbons arriving there, which lets the flows run bar to bar again and keeps each caption next to the bar it describes.
## Hovering lights the inflowing flux
Hovering a group now lights the flux arriving at it, not just its own bar, so you can see where a group's assemblies came from. A group and its ribbons share a `data-node` id and `atlas.js` toggles the class on both — the ribbons are painted beneath every group, so no CSS sibling rule can reach them from the group being hovered. Hovering a ribbon lights the same pair and shows the same tooltip.
## Counts move to the tooltip
The chart no longer prints numbers. A caption is a silhouette, a scientific name and an English name. Percentages and totals appear in the tooltip, over either the group …
Add clade silhouettes, compact navigation tabs, and drop the hover underline (#3)
